Aquatic Ecology of the Tropics

• Overview and brief historical context

• Geodynamics

• Origin of lakes

• Tropical climates 

• Morphometry, zonations

• Limnology was born on the shores of Lake Geneva (Switzerland) and developed mostly in Europe and North America.

• Foci over time: lake descriptions, typology (1920-1930), energy flow problems (1940-1950), pollution (eutrophication) of aquatic ecosystems, aquatic ecosystem restoration.

• This remarkable development in limnology concerned almost exclusively cold and temperate lakes.

Tropical aquatic systems • Don’t get attention from the scientific and management

community they need• Some do, but our general understanding of the ecology and

hydrology of wet ecosystems in this large and heterogeneous region is only developing slowly.

• Little know about extent and distribution of tropical aquatic systems (wetlands in particular)

• No data on rates of wetland losses due to development (thought to be high but are essentially unknown).

• Development pressures appear to be intensifying and the lack of data hinder wetland preservation and sustainable management.

Tropic of Cancer

Tropic of Capricorn

(50 million km2 of land)

Henry Morton Stanley(1841-1904)

Some scientific expeditions to exotic regions of the world that produced sporadic data (preserved specimens of aquatic plants and animals for museums and herbaria of Europe and America).

VictoriaEdward

Kivu

Tanganyika

Albert Kyoga

Rukwa

Following this early descriptive phase of animal and plant collections, more sustained field expeditions in specific localities were organized.

Importance of taxonomy! 

German Sunda expedition (1928) to lakes in Indonesia.Cambridge University expedition to lakes of East Africa (1930-31).Max Planck Institute: Center of Research in Manaus (Amazon).Smithsonian Tropical Research Institute, PanamaInternational Biological Program (IBP-1960s):

Lake George (Uganda) and streams in Malaysia.

• Since 1980s, increased attention (and actually some pioneer textbooks) on the subject of tropical aquatic ecology

• Still, even today, many regions in the tropics remain mysterious areas with unknown diversity.

• Scientific interest in tropical aquatic systems

– species diversity, taxonomy, energy flow, ecology

• Economic and socio-cultural importance

– species extinction, population growth and use of lakes for fisheries, waterborne diseases, drinking water supply. 

• Can tropical ecosystems be understood from principles that apply to temperate systems?

• Some principles easily transfer across latitude (e.g., the response of phytoplankton to light)

• Many others are remarkable different– stratification– nutrient cycling and material turnover rates– biological components (diversity, role of fish)– trophic cascades– floodpulses– growing seasons– ecosystem resilience– management issues

Aquatic Ecology of the Tropics

• Overview and brief historical context

• Geodynamics

• Origin of lakes

• Tropical climates 

• Morphometry, zonations

Geodynamics

Crustal plate boundaries

Earth’s crustal plates and plate tectonics (geologic processes resulting from plate movements)

San Andreas faultCalifornia

The history of continental drift

Rifting A geologic term that describes the process that occurs when land sinks between two parallel faults.

VictoriaEdward

Kivu(2,700 km2, zmax=240m)

Tanganyika(32,900 km2, zmax=1,470m)

Albert Kyoga

Rukwa

ComparisonLake Erie: 25,700 km2, zmax=64mLake Michigan : 57,800 km2,

zmax=280m

Aquatic Ecology of the Tropics

• Overview and brief historical context

• Geodynamics

• Origin of lakes

• Tropical climates 

• Morphometry, zonations

Chapter 11Origin and Ages of Lakes

• Glacial• Tectonic• Volcanic• Riverine• Coastal• Solution• Reservoir

Tectonic

Lake Tanganyika

Graben lakes: multiple faults

Rifting A geologic term that describes the process that occurs when land sinks between two parallel faults.

Lake ChadDepth: 2-3 mWatershed:lake = 604:1

VictoriaEdward

Kivu

Tanganyika

Albert Kyoga

Rukwa

Lake Chad, which once straddled the borders of Chad, Niger, Nigeria and Cameroon, has shrunk by an estimated 95% since the mid 1960s, due to the growth of agriculture and declining rainfall. Image: Unep

Volcanic crater Lakes

Caldera lake: Laguna Boto

Riverine (or fluvial) lakes Oxbow lakes (billabongs)Blocked-valley lakesVarzea of floodplain lakes

Lakes with other origins

• Coastal lakes

• Solution (karst) lakes

• Reservoirs

Wintergarden, Florida

ReservoirsReservoirsHydro power, irrigation, flood control, drinking water supply and now….methane emissions

Kariba Dam on the Zambezi, Zambia/Zimbabwe.